This invention relates to apparatus for, and a method of, monitoring fluid flow through a filter. An example of this is the monitoring of oil or gas flow through a sandscreen in a well.
In unconsolidated sandstone reservoirs within fluid well bores, a sandscreen is normally installed as part of the completion of the well. A sandscreen typically comprises a tubular mesh or perforated metal sheet loaded with gravel. The loading can be done either prior to installation or, preferably, downhole. The presence of gravel prevents sand particles from the reservoir formation penetrating into the well production tubing. In other words, the sandscreen acts as a filter, allowing only fluids through. A problem with such sandscreens is that they can become blocked with impervious contaminants. Consequently, the velocity of the fluid being extracted is lower in the vicinity of the blockage and is higher proximate the remaining clear area. This sets up a pressure differential which could, in time, damage the screen and consequently result in production loss. It is difficult for an operator to detect blockage of the screen as there may not be an overall reduction in flow rate. The blockage may only become apparent when it is severe.
For this reason, it is desirable to be able to monitor flow through the screen. Conventionally, a wire-line tool incorporating a fluid velocity measurement sensor is employed. The sensor is lowered down the well production tubing on an occasional basis; the intervals between measurements are determined by skilled operators.
Certain problems may be encountered with conventional sensors. For example, there is a risk that the well may be damaged whilst the tool is being lowered into, or removed from, the well. Furthermore, operators are reluctant to lower the tool into the well unless essential, thus putting the sandscreen at risk of damage should the screen become more blocked as a result of delay.
The invention provides apparatus for monitoring the condition of a sandscreen in a fluid well system, the apparatus comprising an optical fibre incorporating at least one pressure sensor responsive to a light signal transmissible through the fibre and to pressure exerted on it by fluid flowing through the sandscreen, so that the sensor is arranged to produce a sensing light signal indicative of a characteristic of the fluid flow which, in turn, is indicative of the condition of the sandscreen.
The provision of a sensor in an optical fibre, which has a small diameter, permits the apparatus to be permanently installed downhole. Thus, monitoring of the sandscreen can be carried out continuously, with no risk of damage to the well.
The principles behind the invention are not limited to the monitoring of sandscreens. Accordingly, the invention further provides apparatus for monitoring the condition of a filter in a fluid flow system, the apparatus comprising an optical fibre incorporating at least one pressure sensor responsive to a light signal transmissible through the fibre and to pressure exerted on it by fluid flowing through the filter, so that the sensor is arranged to produce a sensing light signal indicative of a characteristic of the fluid flow which, in turn, is indicative of the condition of the filter.